This invention relates to a loading arrangement in a paper machine doctor, in which the doctor includes a blade carrier and a blade holder fitted to it rotatably by means of an articulated joint. Loading devices operated by a pressure medium are fitted between the blade carrier and the blade holder, to turn the blade holder in relation to the blade carrier and thus to press the doctor against the surface to be doctored.
Generally, the blade holder of a doctor is made in several parts or to be otherwise flexible, so that the doctor blade, which is as such flexible, will lie against the surface to be doctored. In this case, however, the contact force on the actual surface of a doctor blade pressed by means of conventional loading devices varies at different points. This variation appears as a poor doctoring result and uneven wear in the doctor blade.
U.S. Pat. No. 5,279,710 discloses a paper machine doctor, in the blade holder of which there are fine-adjustment screws, in addition to the doctor blade attachment screws. The tightness of the fine-adjustment screws acts on the doctor blade and the screws can be used to try to force the doctor blade to conform to the shape of the surface being doctored. The solution disclosed is, however, complicated and only a small shaping effect can be achieved on the doctor blade with the fine-adjustment screws. In addition, the blade settings cannot be changed during operation, and vibration can cause the setting of the fine-adjustment screws to alter.
The present invention provides new kind of loading arrangement for a paper machine doctor, by means of which the shape of the doctor blade and the force it directs to the surface being doctored can be adjusted in zones during operation.
More specifically, the present invention provides a loading arrangement in a paper machine doctor, in which the doctor includes a blade carrier and a blade holder fitted to it rotatably by means of an articulated joint. Loading devices operated by a pressure medium are fitted between the blade carrier and the blade holder to turn the blade holder in relation to the blade carrier and thus to press the doctor blade against the surface to be doctored. The loading devices include at least one operating device on the loading or the return side, which operating device comprises two or more loading components set one after the other in the longitudinal direction of the doctor. An independent pressure medium connection extends to the loading components, to make the profile of the doctor blade conform to the surface to be doctored, over the length of the doctor.
In one embodiment of the invention there are 3-21 loading components in the operating device. Preferably, there are 5-9 loading components in the operating device.
The loading components are fitted to touch each other, so that they form a loading hose extending over the length of the doctor. There are operating devices on both the return side and loading side of the doctor, the constructions of which essentially correspond to each other.
Each pressure medium connection is arranged to each loading component through its outer surface. Each pressure medium connection may be formed from a flexible tube, which extends from the loading component to either end of the doctor.
The pressure medium connection is arranged by means of tubes fitted inside the loading components, and which extend through the end walls of the loading components. The tubes are arranged inside a stiff metal pipe, which is fitted tightly to the end walls of the loading components.
Each pressure medium connection may be formed from a common feed line and have control valves connected to it. The feed lines may be arranged in the axle forming part of the jointing, or in connection with it.
The loading arrangement according to the invention can be used to load the doctor blade at certain intervals with a desired force. This improves the doctoring result throughout. The loading arrangement according to the invention can also be used to even out the possible uneven wear of the doctor blade. In addition, as the contact force can be adjusted in zones, a good doctoring result can be ensured by increasing the contact force, for example, in the web feeding area. In a corresponding way, it is possible to adjust the roughening effect of the doctor blade on the roll surface.
These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings.